Fuel cells can be configured in numerous ways with a variety of electrolytes, fuels and operating temperatures. For example, fuels such as hydrogen or methanol can be provided directly to the fuel cell electrode. Alternatively, fuels, such as methane or methanol, can be converted to a hydrogen rich gas mixture external to the cell itself and subsequently provided to the fuel cell. Air is the source of oxygen in most fuel cells, although in some applications, the oxygen is obtained by hydrogen peroxide decomposition or from a cryogenic storage system.
Although there are theoretically a limitless number of combinations of electrolyte, fuel, oxidant, temperatures and so on, practical systems include solid polymer electrolyte systems using hydrogen or hydrazine as the fuel source and pure oxygen as the oxidant. A polybenzimidzole (PBI) which has been doped with a strong acid is an example of a suitable solid polymer for use in an electrolyte system.
See, e.g., U.S. Pat. No. 5,091,087 which discloses a process for preparing a microporous PBI membrane having a uniform pore structure by immersing fine PBI particles in a polymeric solution of a high temperature stable matrix polymer to coat the PBI with the matrix polymer, drying the coated PBI particle, and compression molding the particles to sinter the PBI. The matrix polymer is extracted from the molded PBI.
It is known in the art to imbibe polybenzimidazole (PBI) dense films with a strong acid to make a proton conducting media.
Recently, International Patent Application No. WO96/13872, published May 9, 1996, disclosed a method of doping a PBI with a strong acid, such as phosphoric acid or sulfuric acid, such that a single phase system is formed, i.e., acid is dissolved in the polymer.
Even in view of the advances in the art, the performance, high cost and processability of suitable polymeric electrolyte materials remain important considerations in fuel cell construction with respect to polymeric media for fuel cells.